Azimuth reference device



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May 26, 1959 R. B. BLlzARD l AZIMUTH REFERENCE DEVICE Filed Dec'. 24, 1953 HH.. N w

May. 26; 1959 R. B. BLIZARD 2,887,733

l AZIMUTH REFERENCE DEVICE Filed Deo. 24. 195s e sheets-sneet 5 R. E. BLIZARD AZIMUTH REFERENCE DEVICE May 26, 1959 6 Sheets-Sheet 4 Filed Deo. 24, 1953 Il INMI l L x 1 Sud lNvsN-ron ROBERT EBA /ZA RD y BY Y v 7 Z/ORNEYM May 26, 1959 R. B. BLIZARD AZIMUTH 'REFERENCE DEVICE 6 Sheets-Sheet 5 Filed Deo. 24, 1955 May 26, 1959 R. B. BLlzARD AZIMUTH REFERENCE DEVICE INVENTORy ROBERT /-BL /ZA RD 6 t e e h q H S L e e h S 6 W Il 4 w c M U w S x T m 5 o l w@ hvQB Mw vH 4S 4. Y 2 o I o 7 no m I d .0J m l .l F

United States Patent Wim-3 c -AznyrUrH REFERENCE DEVICE man Bini@ d, Siam i Cw?, si'stgnr" to Sperry un 5 "i Application December 24, 1,953, Serial No. 49%118 s1-uen@ 1111s .invention relates tv er1-instrument Off the gYfQ- seaeic Gemss was Saeislrdeslg 'i taining an 'sa W Y. i.,-.. ,il a sin 1t is the present presti?? t9 sensei i2@ IY; gue rom one rnastervposition, i.e., for all guns to zig to .the presentiin enton, 1155999@ 19 elimflfe fills ,time consuming and .dlllcult prfedlre lZY'PIOXld sun with its .owngyro-Compass SQ .that ih? 19,35??? S can transmit the bearings of the frgtwih f??? the 'meridian (suitable allowance being metia 0f 999m@ for Iparallax corrections). Unfortunately, the'stand'ard gyrolcin'pass cannot beused successfully lfontlgis purpose Vbecause it requires Abetween 'one and tvvo hoursf'or more to settle on the meridian after Istarting up afa random position, so thatY if astandaid' gyra-compass is ernplo`yed `for thel purpose, no time would be saved in"g'etting fthe `battery `in to operation. r

i Myinventionftherefore, is directed toward devising an instrument'of the gyroscopic cnipass ty`pe which can ,be 'ibroughtto -a`nd` settled onihe meridiany in a matter of a fewfvmintes, afterV` Whichit' vvill'cdntinue to ,hold the "meridian4 with"ektreme'accuracy inspite' of the shocks f gunfire.' Other oljecf'so'f tlie'invention are jto improve "gyrsopic instruments "of this `tj/pe`so s to `be Virtually "unaffected b'theolt's andjars df the rgun-carriages and Astljlia'sic reference device, I employ a gyroscope otE` 2,887 ,783 Patented May 26, 1959 ICC 2 i oV=The vertical componentl of the earths rotational velocity at latitude M i.ef.,'the component `oflthe'eartls angular velocity Which is normal to the earths'surface atl'latitd Xfherein"'abbreviated' as' the vertical: earth rate?v *fr* ff' t'.- mm., l a# clinat' 'zonfl '-l f. =^i`zinuth angle :between the gy-ro spin axis when horizontaland the meridian, and is also `referred et@ herein n angle of the gyro spin axis to the liori-I From the above definitions, it will be at once apparent thatf'- w1 I v 2' ,.-z ,vafm oH=w cos A (1) EquationU S vtherefore` is"acci1r'ate"'within v*the fi' mred 11inits of the device, and can*"thereforey b asiliiie zero-by 2introducing a constant torque conteractingthat Idueto wv.--

Since the latitude is known, it follows `that by deter- .mining @"or the tilt perunittime the error angle @may '.ebe'eomputed;` To measurel the-tilt rate, Iemploya. sensi- "ftive damped pcndulumf,'preferably thesarne pendulumas I employ to generate the meridian-seeking torqueotf the compass whenoperating asta-true'gyro-compass, and ob- 'tain'ithe laverage-tilt -an'gle per unitttime; or-theaverage 'tilt rate over-"a predetermined 'timeintervaL -Since the T purpose of'the invention is to l secure quick n cling ofthe meridian, and since-the rate -Yof tilt oflthe'gyroissmall, I r,lla've devisedv an-employi a very-sensitive pendulum; capa- Figs. 7 and 8 are two diagrams showing how a sine curve is used as a weighting function in the determination of tilt rate, Fig. 8 illustrating a combination of curves ,A and B of Fig. 7 and showing that the curves are not yaffected by the starting point in the cycle, if one complete cycle is employed.

The 'gyro-compass employed is preferably of the type zin which the meridian-seeking and damping torques are Because of the random nature of the output of the pene duilum, the calculation of the error is improved by introducing a weighting function which allows certain selected sections of the measuring interval to contribute more to the total integral than other sections and thus to be more important to the average. By choosing an odd function as the weighting function, its own over-al1 contribution to the integral can be made zero. Such random motions in a parked vehicle have been found to be in the nature of a series of very short and rapid motions, and therefore, resemble noise as this expression is used by radio technicians. By mathematical investigation of the curves and equations involving averaging by the root mean square method, I have determined that a sine curve as a weighting function gives a very close approximation to the best theoretical curve to use and, therefore, I employ a sine curve as a preferable form of weighting function to be employed.

` ySince the rate of tilt is proportional to the azimuth .error p) and inversely proportional to the secant of the Alatitude (sec I derive from these factors a signal which displaces the synchros in the computer through an angle `representing the computed error arising during the evaluation.l At the end of the evaluation period, a switch is thrown connecting the synchros in the computer to those Lthe positions of the synchrosdo not agree. This signal causes a strong torque to be applied about the horizontal axis of the gyro until the synchros at the gyro and in the computer agree. At the same time, a strong torque is also has now been set upon the meridian in a level position and is ready to resume operation as a gyro-compass, which i its done by throwing another switch.

also preferably employed as the first stage of the operation, that is, the device is preferably operated as a `gyrocompass While the :gun is moving up to position so that when the-gun arrives at its position the gyro will be runt and in full operation and usually positioned Within about live or six degrees of the meridian.

' jFig.A 3 represents the several elements as connected during what is known as the preparation period, which is started inmediately after the gun has assumed its position in the battery and is stationary;

Fig. 4 is a similar block diagram showing the connections for the several elements during the computation or evaluation period, during which period the rate of tiit is determined; Fig. is a similar 'block diagram of the connections for lthe elements during the correction period, at which time a torque is applied to the compass toV correct its position j in azir'nuth to that determined during the evaluation periodyand asecond torque is applied to level the compass;

Fig. `6 is a side elevation and wiring diagram of the pendulous controller; and

derived from electrical signals controlled by a small gravi- 'tational factor such as a damped pendulum or liquid level, a gyro-compass of such type being disclosed in general in the prior copending applications of Frederick D. Braddon, S.N. 261,508, tiled December 13, 1951 for Gyro- Vori'thegyro, thereby producing an error signal in case K;

i appliedabout't-he gyros vertical axis, controlled from the4 y pendulum to again level the gyro. The gyro, therefore,

erate solenoids.

scopic Instruments, now U.S. Patent 2,729,107 dated Jannary 3, 1956, and Vacquier, Cope and Proskauer, S.N. 261,524, tiled December 13, 1951 for Control Systems for Gyroscopic Instruments, now U.S. Patent 2,729,108, also dated January 3, 1956. Such a compass is illustrated diagrammatically in Fig. l, the gyro rotor 1 being vshown mounted for spinning about a normally horizontal spin axis 2 in rotor case 3, which in turn is mounted for freedom about a horizontal axis 3' in vertical ring 4. The vertical ring in turn is mounted for orientation about a vertical axis 5 within the follow-up or phantom ring 6 which is driven by an azimuth motor 7 geared to azimuth control transformers 40, 42 in the integrator 30. An electrical or azimuth torquer for imparting meridian-seeking vtorques to orient the compass is represented at 10 and a damping or levelling torquer for applying a torque about 'thel vertical axis is represented at 11.

The primary source of supply is single phase A.C. rectitiers 112 and 113 being shown in some instances to op- In a few other instances, D.C. is employed where so marked. Ground returns are shown to simplify the diagrams.

The preferred form of pendulum or gravitational controller is shown in Fig. 6 and comprises a pendulum bob 12 of insulating material suspended by a line wire or ilar element 14 within a tube 16. On the north and south sides of the pendulum, as mounted on the gyro seusitive element, are two parallel metal plates or strips 18 and 20, the tube being lled with an electrolyte of predetermined viscosity to damp the pendulum. Preferably, the tiilt of the pendulum is limited by the offset extension 19 from the strips to about $30 minutes so that the pendulum is not allowed to tilt with respect to the plates more than the amount normally encountered in a meridian-seeking cycle, thereby reducing ballistic deflection and preventing undue disturbance during gunfire recoil. The plates and lar element are placed in a bridge circuit, las shown in Fig. 6 of the drawings, alternating current from transformer 22 being supplied to the two plates, and an output amplifier 24 is connected between a mid-point 28 on resistors 26 and the lilar element 14 so that the tilar element acts as a probe of the potentials at a point between the two plates which is displaced with tilt and a voltage is thereby applied to the amplifier whose magnitude is a measure of the magnitude of the tilt of the gyro spin a'xis from the horizontal and whose phase varies with the direction of such tilt.

Because of the difficulty in following the wiring connections employed for each of the four modes of operation of the device, I have shown by separate diagrams,

Figs. 2, 3, 4 and 5, one foreach mode of operation, only.

disagreement. The outputs thereof are mixed in the coarse-fine mixer 82 to furnish a `single signal to lead 84, through the contact C.T. in switch 23 and the iirst contact in the zeroing relay 25, and back to the amplilier 32, thus constituting a servo loop which serves to align the orientation of tine and coarse control transformers 40, 42 with the azimuthal orientation of the gyro spin axis. A mixer suitable for use herein is shown in the patent to McCoy and Kusto No. 2,620,441, dated December 2, 1952 for Electronic Signal Mixers. As soon as, however, the signal disappears in the output of amplifier 32, solenoid 31 becomes deenergized, indicator 110 reads zero, showing synchronization, and the four switches are moved to the left in Fig. 3 whereupon the signal lamp 51 is lighted, as shown in Fig. 4, to show the preparation period or mode is completed and the device ready for the computation period or mode of operation.

The correction for vertical earth rate wv is still retained in the preparation period (as it is in all phases) so that the gyro azimuth error will remain constant in spite of the earths rotation during the preparation and computation periods (see Equation 6). Therefore, if any gyro tilt appears, it should be due solely to the compass being olf the meridian. At the end of the preparation cycle and the beginning of the computation cycle, the gyro is level, near the meridian, and operating as a free gyro corrected for the vertical earths rate component.

The device is now ready for the third mode of operation, i.e., the computation or evaluation mode illustrated in Fig. 4. This mode is initiated by closing switch 90 which starts timer 92. It is during this period that the mean tilt per unit time is determined from which the azimuth error of the compass is computed according to the theory heretofore outlined. In this stage, it will be seen that the meridian or azimuth torquer 10 is still controlled by the earths rate resolver 76 so as to keep the gyro azimuth error q constant by eliminating the azimuthal effect of the earths rotation w on the gyro. Since the rate of tilt of a free gyro depends not only upon the azimuth error but also upon the secant of the latitude (see Equation 6), a latitude correction must also be employed to determine azimuth error from nate of tilt. Therefore, the signal from the pendulum is again fed through amplifier 24 into the same latitude computer 37 as employed in the compass phase of Fig. 2, which has a cosine resolver `66 positioned from the latitude setting handle 68 to introduce the reciprocal cosine factor `cos A again by virtue of the feedback connection around ampliiier 56. Hence, the output of amplifier 56 may also be expressed as a function of sec A which, it may be observed, is one of the known, settable and hence constant terms of Equation 6. A preferred form of secant computer is shown in the above-mentioned patent to Herbert Harris, No. 2,546,156, dated March 27, 1951, for Computer Apparatus, in which details of this type of resolver may be found. Reference may also be had to the prior application of Edmund B. Hammond, Jr., Serial No. 323,437 for Gyro Roll Compensating System, filed December 1, 1952.

The means by which the tilt per unit time or tilt rate is derived will now be described, reference being made to Figs. 4, 7 and 8. In Fig. 7, the wavy curve represents the signal from the tilt pendulum 12 and is shown as increasing from some initial angular value, which is initially made zero during the preparation mode, to some larger value at the end of a predetermined time period T, which, in the present case, is four minutes as determined by the timer 92 of Fig. 4, as will be described below. The wavy character of the signal illustrated by curve A is due to random accelerations or noise produced by vehicle movement. The derivation of tilt rate from measures of tilt angle is based on the principle that if there are no other accelerations acting on the pendulous mass except that due to gravity, a measurement of the difference in the tilt at the beginning and end of a predetermined time interval divided by the time interval will provide the desired measure of the average tilt rate. If a continuous measurement of tilt is made over the time period T, the problem is lsimpliied because the function to be averaged may be integrated with respect to time with the result being divided by the time. In the particular case under consideration, however, where random accelerations do act on the pendulum over the entire measuring period, the accuracy of the latter measure is improved by introducing the above de'- scribed weighting function which allows particular sections of the measuring interval to contribute more to the total integral than others. Mathematical analysis has shown that the theoretical weighting function applicable in the present instance has a form very similar to a sine wave so that in order to simplify the practical application a sine wave is used. This curve is shown at B in Fig. 7. It should be readily apparent that since the weighting function is in the form of a sine wave its effect alone on the output of the integrator 30 will be substantially zero. The curve C illustrated in Fig. 8 shows the character of the tilt signal after it has been multiplied by the sine curve weighting function. Thus, in the computation mode of operation, the final angular position of the output shaft of the integrator 30 is proportional to the average tilt rate of the gyro which, in accordance with Equation 6 above, is equal to the azimuthal error between the spin axis of the gyro and the geographical meridian.

The timer mechanism (Fig. 4) comprises essentially a motor 94 run at a constant speed and connected through reduction gearing to one face 96 of `a slip friction clutch. The other face 97 is normally locked by lock pin 98 so that it is held against rotation. To the shaft 97' of face 97 is secured a rotatable winding of the sine resolver or sine curve multiplier 58. When the button is momentarily pressed, the solenoid 100 controlled therefrom withdraws the lock pin 98 so that the face 97 starts to rotate at a speed of a quarter revolution per minute so that in four minutes one complete revolution will have been made. At this time a detent 102 on said clutch face 97 closes the switch 104. During this interval the modified tilt signal, further modied by the sine wave weighting function as described above and appearing on leads 106, has been causing the integrator 30 to operate, thus shifting the position of the control transformers 40 and 42 through an angle which is proportional to the tilt of the gyro at time zero, i.e., the beginning of the computation mode which is zero, and its tilt at the end of the four minute time period. This angle is therefore proportional to the average tilt rotate 0' of the gyro spin axis, that is, so many degrees per minute as described above. This angular position of the control transformers therefore represents the computed error p of the compass in accordance with Equation 6. The closing of switch 104 terminates the computation period and initiates the correction period at which time the error computed and stored in the control transformers 40, 42 by operation of the integrator is actually put into the compass.

In the correction period (Fig. 5), the synchros 9 and 9' on the gyro are connected to the control transformers 40 and 42 in the computing device which has, of course, been displaced during the four minute computation period by the output of the sine resolver 58. If there is any disagreement, therefore, between the gyroscope which has been operating as a directional gyroscope and the azimuth position as indicated by the cornputer, an error signal p is produced actuating compass error indicator and also fed through mixer 82, switch 74 yand earth rate corrector 76, into the azimuth torque tnriitisr 80 and apnlieslte tss .immette ai) birtii Y@if signal 1 results a greatlyimfeasedthat the agregan be 111e levelling tsr-aua 11.118. rendered responsive t9 the v:and .the nant t9 .levelling torquer meridian Pasivos as 91111 by @maite l the 99.19B.

pendulum nel site@ assigning at ..1.1 and@ of operation to quickly rellevel the gyro spin axis. This is automa ally acsaalilis@ with the slaags gf detentoperated s itch 10,4 in the timing mechanism 92. Closing of this switch energizes relay solenoid 114', yswitch 'ar-m 1 ^14 being-movedto vthe .left into contact with contact `101 thereby energizing `relay .17. Relay 17 in tum moves switch to the right thereby establishing a direct connection between `the output of .pendulum pre-amplifier 24 will he .that .in the canadian .fasse :te

since the resistor 64, which provides the normal levelling sensitivity, is shorted out. In this manner, the gyro is quickly brought onto the meridian, level and ready to be switched back to operation as a normal gyro compass, this normal mode being illustrated in Fig. 2 as hereinbefore described. At this time, switch 23 should be moved to its down or L.S. position and the zeroi'ng button 29 pressed or closed. This operation serves to place the linear synchro 38 in follow-up on itself and thereby zeroes the integrator 30. Thus, both indicators 86 and 110 should read zero, the system then being ready for normal compass operation. The main azimuth referencecompass switches may then be thrown back to their compass positions thereby completing the entire cycle of operation ofthe system.

From the foregoing, the operation of my improved azimuth reference device should be apparent. While my device is primarily a gyro-compass having all the characteristics of an accurate gyro-compass, not only may it also be operated in the manner described as a quick means for setting the compass on the meridian but, when so employed, it constitutes in reality a new method of locating the meridian and hence constitutes a new form of azimuth reference device. In this device, the gyro is not north-seeking, but the meridian is determined by measuring the rate of tilt of the gyro over a predetermined period and from this, determining the angle that the device is off the meridian, from which, of course, the meridian may be determined assuming the approximate latitude to be known. Since during this time the gyro operates as a free gyro, it is unaifected by vehicle speed and hence one large source of error in gyro-Compasses is avoided. Since the vehicle speed error becomes quite large in aircraft, my novel form of azimuth reference device has a marked advantage for use in high speed aircraft over the standard form of gyro-compass.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of quickly setting a gyro-compass on the meridian which consists in eliminating meridian-seeking and damping controls for a predetermined period, but continuing to apply a torque about the horizontal axis to eliminate the effect of the vertical component of earth rate, producing a signal proportional to the average rate of tilt of the gyro taking place during said period, calculating therefrom the compass error causing such rate 0f tilt at that latitude, correcting the compass for such passed to the levelling torquer ampliiier unattenua ed .enst and teal-,Y incudine-@estira sammle 2 Ih setlist sf .Quietly .Setting a .gyra-Campen an ab at ttihvaieital.

aoanfstitot. armate portional to the average rate of tilt of the gyro .y lng glass .dun-ing :t2-.litigated selulatiag fhsfsffsai the. s0111- aass erratas-vials Such rate gf tilt at .that Waise-09.1"- rze ing the'gompas h error, again levelling .tire

y rs-sumisa .tiendan-leek@ .and

corripass,m and daggie. .scattatae method of altislsly Setting a gytozvlapass .0.11 Lian W 9.1.1 @asista insita-inning merid'.

alanine@ .the fsffeat .ot-'th vettige @nagaan of earth rate, producing a signal proportional'to the average rate of tilt of the gyro taking place during said period secured by employing a sine curve weighting factor, calculating therefrom the compass error causing such rate of tilt at that lattitude, correcting the compass for such error, and finally resuming meridian-seeking and damping controls.

4. In an azimuth reference device, a free gyroscope, means for applying a torque about the horizontal axis thereof proportional to the vertical component of earths rate whereby to maintain the azimuthal position of said gyro substantially fixed, means for producing a signal proportional to the tilt of the gyro about said horizontal axis, means for averaging said tilt signal over a period of time whereby to produce a signal proportional to the average rate of tilt during such period, said latter signal being proportional to the azimuthal error of the device, and means responsive to the latter signal for resetting Said device in accordance therewith whereby to eliminate said azimuthal error.

5. An azimuth reference device as claimed in claim 4, in which said averaging means includes a weighting factor having means for multiplying said signal by one cycle of a sine curve.

6. An azimuth reference device comprising a gyrocompass having a gravitational factor and an electrical azimuth torquer normally controlled thereby for applying a meridian-seeking torque about the horizontal axis of the compass, a levelling electrical torquer also normally controlled thereby for applying a damping torque about the vertical axis thereof, an earth rate resolver means for also controlling said azimuth torquer in accordance with the vertical component of earth rate, and means for temporarily eliminating the control of said azimuth torquer and the levelling torquer from said gravitational factor but retaining the control of said azimuth torquer from said earth rate resolver means, whereby the device may be made to operate at will as either a gyro-compass or directional gyro, each corrected for the vertical component of earths rate.

7. An azimuth reference device as claimed in claim 6, also having a latitude cosine resolver, means operated therefrom for modifying the control of said azimuth torquer to normally maintain the period of the compass constant for all latitudes, and means also operated therefrom for maintaining the rate of tilt due to the horizontal component of earths rate constant, regardless of the latitude, during the directional gyro mode of operation.

8. A meridian-finding device, comprising a directional gyro, means for measuring the tilt thereof about the horizontal axis of said gyro, means including a cosine resolver for modifying said measure in accordance with the cosine of the latitude, means for deriving from said modified measure the average rate of tilt of said gyro at Said latitude, said modified measure being proportional 'aser/,vas

to the angular deviation of said 'device from the meridian, and means for controlling said gyro in accordance lwith said average rate of tilt whereby to eliminate said angular deviation and thereby place said gyro on the meridian.

9. A meridian-iinding device as claimed inclaim A8 also having means for correctingsaid gyro for azimuth drift due to the vertical component of earth'rat'e before, during and after the operatingrof said rate' of tilt de. riving means. `1 I" 10. A meridian-finding device as claimed in claim `9, in which said rate of tilt deriving means includes a single cycle of a sine curve as a weighting factor which is multiplied by the output of the cosine resolverl l1. In a meridian-seeking gyro compass-systemfa-gyroscope having freedom about`vertica1' and` horizontal axes, means for providing a signalin accordance with the vertical component of earths rate, means responsive to said signal for prccessing said gyro about lsaid vertical `axis in accordance therewith whereby to maintain theugo 'tional to the tilt of the gyro about said horizontal axis, computer means responsive to said tilt signal for providing 'a' correction lsignal proportional to the averagel rate of tilt of the gyro about said horizontal axis, and means responsive to said correction signal for precessing said gyro about said vertical axis in accordance therewith whereby quickly to place said gyro on the meridian.

References Cited in the le of this patent UNITED STATES PATENTS Haskins May 6, 1947 2,677,194 l Bishop May 4, 1954 OTHER REFERENCES l Practical Analysis (F. A. Willers), published by Dover Publication, Inc. (New York), copyright 1948. 

